Steve, I haven't changed my v-drive oil or transmission fluid yet but I did recently do the engine oil in my new-to-me Launch 24. I have the 8.1 but the general process should be the same. The 8.1 uses straight 40 weight so it was essential to run the motor up to temperature to get the oil to flow out. The 15-40 that the 350s use should flow better but I still recommend it. Your boat should have a long oil drain hose coming off of the pan that can be threaded out through the transom drain plug and opened to let the oil run out into a bucket. Your trailer will need to be on a flat surface for this to work -the engine slopes toward the bow and then that hose needs to slope toward the stern. This is due to the V drive configuration. If you put the trailer on a slope, it will mess up one of those angles. I found it was a lot easier to just get an oil extractor and pump the oil out of the drain hose.
The second learning I had was in regards to the oil filter. I have the remote oil filter, I think this is primarily an 8.1 thing but is available on the 350s as well. The angle in the mounting bracket causes the filter to come into contact with the bracket ever so slightly. This will make it impossible to spin the filter off, even with a wrench, so you'll need to loosen the bolts that attach the filter mount to its support bracket just a little and the filter will spin right off.
2006 Launch 24 SSV Gravity Games w/8.1